[mesmark]

I do something similar to that. I draw a structure like a old western cowboy jail house with no cell to start. Then as the students make mistakes, I draw the four walls of the square and then add two vertical bars and that's the end.

If the jail is completed, I throw them into it. I then draw a little sad man inside. It's even better if you have a place in the room designated as the 'jail.' This is the place where losers must go and sit, write something or read something until they are broken out or the game is over.